Adjustable electrical resistance apparatus



March 23 .1926. 1,577,456 F. M. ENDE ET AL ADJUSTABLE ELECTRICAL RESISTANCE APPARATUS Filed April 2'5, 1924 2 Sheets-Sheet 1 gii 7. 5

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March 23 ,192'6. 1,577,456

' F. M. ENDE ET AL ADJUSTABLE ELECTRICAL RESISTANCE APPARATUS Filed April 25, 1924 2 Sheets-Sheet 2 ATTORNEY Patented Mar. 23, 1926.

UNITED STATES PATENT .oFFIcE.

FRANK M. ENDE, OF NEW AND PERCY A. E. ARMSTRONG, OF LOUDONVILLE,

NEW YORK.

ADJUSTABLE ELECTRICAL RESISTANCE APPARATUS.

To all whom it mag/concern:

' Be it known that we, FRANK M. ENDE, a

citizen of the United States, and a resident of the. borough of Manhattan, city, county, and State of New York, and PERCY A. E.

ARMSTRONG, asubject of the King of Great Britain, and a resident of Loudonville,

county of Albany, and State of New York, have invented a new and useful Improvement in Adjustable Electrical Resistance Apparatus, of which the following is a specification.

Our invention relates to adjustable electrical resistance apparatus adapted for many uses, including, forexample, rheostats, potentiometers, grid leaks, .audibility meters, etc. According to the present invention practically continuous variability or adjustability is secured by moving relative to one another an electrical resistance element and a contact member of fluid metallic electrical conducting material, such as mercury, for example, thus doing way with the wiping mechanical contact members commonly used in prior apparatus, making the operation completely smooth and noiseless, and making possible the enclosure of all the members with no exposed moving parts and avoiding the liability of corrosion. and the like attendant upon exposed working parts.

The accompanying drawings illustrate embodiments, of the invention, but it is to be understood that same are only for the purpose of afi'ording an understanding of the invention and not for limitation of its scope.

In said drawings, Fig. 1 is a cross-sectional view of a resistance apparatus set in a panel of insulating material. Fig. 2 is a rear view of the apparatus shown in Fig. 1. Fig. 3 is a section on the line 33, Fig. 1, looking in the direction of the arrows. Fig. 4 is a section on the same plane indicated by line 4-4, Fig. 1, with the arrows looking in the opposite direction. Fig. 5 is a view similar to Fig. 4, but with the parts turned through an angle of substantially 180 de-' grees as compared with Fig. 4. Fig. 6 is a detail viewshowing a modifiedform of mercury' controlling bafile- Figs. 1-6 all illustrate the casing as made of insulating material and the resistor of carbon, graphite or the like material. Figs. 7-12 illustrate a tallic material. Fig.7 is a sectional view of modification inwhich the casing is of me Application filed A ril 23, 1924. Serial 110,708,324.

such modified form on the broken line 7--7,

Fig. 8, and Figs. 8'and 9 are rear views with parts broken away of the device shown in Fig. 7. Figs. 10 and 11 illustrate a further modification generally similar to that of Figs. 7-10 with the resistance material disposed on a disk of cardboard or the like. Fig. 10 is a sectional view of such modified form taken on the broken line 10-10, Fig. 11, and Fig. 11 is a rear view of the device shown in Fig. 10. Fig. 12 is a detail view showing a wound resistance in combination with a mercury contact. Figs. 13 and 14 are respectively side and rear views-of apparatus as illustrated in any or all of the views previously referred to, with the addition of 'an anglebracket for stationary binding tight joint, care being taken to keep casing 10 mercury tight in all parts.

Casing 10 contains therelatively adjustable elements and is adapted to be rotated bodily as by means of the shaft 16 journaled in the bearing sleeve 18, which may be secured in the panel 20 by the nut 22, and provided with any suitable operating means, as the knob 24 made of non-conducting materiaL- A dial or other customary position indicator may be associated with the turning means, if desired. A washer 26 is shown encircling sleeve 18 and held by nut 22, and a stop arm 28 projects from washer 26 to cooperate with a stop lug .30 on casing 10 and limit the rotary movement of the casing.

The resistorelement 32 and the mercury contact 34 enclosed within the casing 10 make up the relatively adjustable parts, and relative adjustment between the mercury contact 34 and the resistor element 32, which latter is fixed to the casing and extends into the mercury pool, is obtained by rotation of the casing and resistor 32, the mercury con tact 34 being kept stationary at the lowest point of the casing by gravity. In theform shown in Figs. 16, the resistor 32 is in the form of an interrupted annulus of electrical resistance material, such as pressed up carbon, graphite or the like, though other forms of resistance elements, such as the wound r6- tricalconducting members extending to the exterior of the casing 10, and in the form shown binding post screws 36, 38 serve to support resistor 32 by .itsseparated ends within the casing 10 and extend to the back of the casing where they may serve as binding posts for making electrical connections.

Means are provided for establishing an electrical 'counection between the -mercury contact 3- and a lead wire or the like 40 in the various rotative positions of the casing 10. in the form shown. a metallic disk 42' of brass or the like material is provided for this purpose. Metallic material used in contact with mercury should be of such nature as not to amalgamate therewith, as, for example, brass tree from lead gives good results. The brass disk 42 extends into the mercury pool 31- and in the form shown is secured to the threaded stem at of shaft 16 by lock nuts 46, 16 and stem ll extends through the casing caplet and serves as a binding post tor connection of wire 4().

Provision is made for preventing the scp-' arated ends of the resistor 52 from being shorted by the mercury contact, and in the form shown, a septum or dam 18, which may be of various forms, but is here shown of radial formation is provided 'to extend across the chamber 10 of casing 10, between the ends 32 and 32 of resistor 32, and serves to keep the mercury contact pool M, which may be in contact with one of the ends of rc-f sistor 32, out of contact with the other end when the casing is turned, for example, into the position shown in Fig. 5, where the rotation of the casing may be stopped by the lug 30 coming into contactavith the stop arm 28. To make room forthe bafile or dam 48, the brass disk 42 is notched out or cut away, as shown at. 42, Figs. 1 and 5. Should the stop members 28, 30 be omitted sothat the casing can be turned-all the way around, it

may be desirable to extend the end of the sept um horizontally on each side in substantial] y a T-form, asshown at 48, 48", Fig. 6.

Seine of the many possible constructional modifications are shown in Figs. 7-11, in

which the mercury contact member is received in a metal casing l0 to which the central binding post 50 is directly secured. The metal casing is made mercury tight, as b the parts being spun or soldered together.

he resistor 32 of Figs. 7 and 8, which is substantially like that of Figs. l-6, is insulated from the metallic casing 10' as by passing the binding post and resistor supporting members through the insulating bushings 52, 53. An alternative way of preventing bridging or shorting of the resistor connections isshown in these figures and conslsts of separating the ends of the resistor to such an extent that while the resistor makes ample contact with the mercury when the former is immersed therein, the mercury does not come into contact with more than one end of the resistor at a time, and intact may in some positions be out of contact with both of the'resistor ends, as shown in'Fig. 9. \Vith such arrangement the battle or dam 48 maybe dispensed with. y

In Figs. 10 and 11 the resistor element turning with the metallic casingditfers from 7 "studs or spacers 58 to keep it in preferably centralized position between the. casing walls. Use of cardboard or the like is efhcient and quite inexpensive. \Vhile tle disk 56 may be a complete circle, it desire with the resistance-material extending somewhat less than all the way around, it is preferably formed as a major segment of a circle with a small part 56* cut away to imsure the prevention of short circuiting the resistor.

The leads from the casing 10 may lead direct to thevarious parts to which they are tobe'connected, or, if desired, stationary terminals may be obtained, as by substitutin for .washer 26 the bracket 60 of Figs. 13 and 14, to which is.secured the stationary binding posts 62, 64, 66, which are connected by wires (38, 70 and 72 to the instrument binding posts 74, 76, "8. The insulating strip 80 to which the binding posts are connected is extended toward the casin for a distance beyond the binding posts, as indicated at 82, Fig. 13, so that if the casing s of metal and if it becomes loosened, it will not getagainst the binding posts and thereby produce a short circuit. In case the'bracket 60 is electrically connected with the mercury contact without the use of wire 70 the binding post y 7 6 may be mounted directly on the bracket 60 and wire 70 dispensed with.

It will be. understood that the forms .shown are only for illustration and afiordused, if desired, part or ,all of the terminals may be' used as desired for various uses, as potentiometers, rheostats, etc., and various other modifications can be made.

We claim:

l. A. variable electrical resistance device comprising a substantially cylindrical casing of insulating material, a contact pool of mercury therein, a resistor movable progressively with'respect to the mercury upon the casing being angularly moved and a baflie plate in the casing. 2. In. an electrical resistance device, a mercury tight casing, a. part a1mularelectrical resistance clement therein, a mercury contact in the casing, and a bafiic in the casing between the ends of the annular resist- .lnce element.

3. In a variable electrical resistance device, a rotatable casing, a mercury pool therein, a. disk of electrical conducting material dipping within the mercury to produce an electrical contact in various rotative positions of the casing, and a resistor rotatably in contact with the mercury pool held stationary by gravity as the casing is turned on its axis.

4. A revoluble casing, a resistor ele'n'ient having substantially the form of an interrupted annulus, electrical connecting means supporting the resistor in the casing by its ends, a pool of mercury 1n the casing and kept at the bottom thereof by gravity, elec,

trical connecting means in contact with the mercury as the casing is rotated, and abafile or dam for the mercury extending across the casing between the ends of the resistor.

In a variable electrical resistance device, a mercury tight hollow casing of insulating naterial, a shaft. extending therethrough, a disk on-said shaft, a mercury contact pool maintained at the bottom of the 'asing by gravity with the disk extending thereinto to complete an electrical contact, a part annular resistance element within the casing and turning therewith, whereby continuously'variable contact is made with the mercury, a battle extending across the chamber in the casingbetween the ends of the resistor element to prevent the same being short circuited by the mercury, and a stationary member provided with binding posts connected respectively to the ends of the resistor member and to the disk.-

In testimony that we claimthe foregoing, we have signed our names hereto.

FRANK M. ENDE. PERCY A. E. ARMSTRONG. 

